I'd be glad to explain.
DS appeals to
1. Hardcore gamers
2. Softcore gamers
3. Adults
4. Children
5. Nintendo fans
-All 5 of these groups buy games. Nintendo fans and hardcore gamers probably buy the most, but children who only have a DS and no console may buy alot.

PSP appeals to
1. Hardcore gamers (mostly looking to buy ports on games they missed and some original titles)
2. Pirates who want to steal PSP games, and emulate old games, and maybe listen to movies/music
3. people looking for a movie/music player who may want to play a game of two for variety
4. Sports/FPS fans who want to play these 2 genres on a handheld
5. Sony fans

PSP appeals to about 1/3 as many people as DS does. Of these people, only Sony fans and are going to buy alot of games. Sports/FPS fans will buy some; media people will buy a few, and a few hardcore gamers buy alot but many just pirate.

What everyone else said.

Although I think the main reason is that it basically plays games that everyone already has on their PS2s, so what is the point.

There is really no need to pirate though, at least for me. I have already played NES, SNES I have played some and can get the rest on Wii for about $40 once they come out. Genesis just buy Sega Genesis collection for $20, and then there are about 5 other good compellations on PSP. I think Sony needs to make a PSP2 only because of piracy. If there was no piracy, Sony could of kept the PSP for ten years and had it competing with DS2. Might as well make a new one though; hack proof and more media and with a 2nd analog nub...

How'd you end up with only 2 NES games?

Me, I had like... 50 NES games and 4 GB games.

Well 4 memorable ones anyway.  I actually think i have like 8.

But i mean outside Kirby's Pinall and Mario Land they sucked.

The bolded word in my post.

@SC: Sorry, I meant 80%

1. Piracy: This is the biggest problem. I mean honestly you can buy books of how to do various things with your PSP that a illegal on websites and occasions bookstores.

2. The Battery Life: The second biggest problem is the 6 to 8 hour battery life max with the PSP brightness and what have you all the way up. Pending on what game you are playing 15 minutes or more(less as well) can be lost in that time. Compared to my DS which has 10 hours of life, which equals 10 hours of gameplay since there are no loading screens.

3. The price of games: For the most part you can get a typical DS game for anywhere from $5- $10 cheaper then the PSP games. Also DS games most generally will go down faster. In addition to that alot of people that own console systems can pick up a game for 360 or Wii for the same price as a PSP title. (PS3 titles to)

Those 2 were bundled.. did not see any reason to buy more games for nes back then. I owned master system and C64 so NES did not get a lot of attention. :) Even though I loved mario as a kid. I am from a big family and we had only one tv. So of course I loved my handhelds (GB&GG). I owned something like 20 Game Gear games.. actually I still have them somewhere. :D

It's only by 2 games, and I could see the ds surpassing that at the end of this month or beginning of next month. It just has so much support comming to it compared to the psp.

Piracy , lack of quality games , lack of advertisment , lower install base , tons of crappy ports from the first part of the PSPs life , slow release schedule ... these are the main reasons .

Still , there are tens of PSP games that managed to sell a lot , just by staying months in the 1-5k region/week :) So developers usually will expect to get the development budget out a bit later than fom other systems :)